[TowerTalk] 4 SQ WX0B box

[Jim Lux]

At 05:28 PM 11/18/2004 +0100, Jan Erik Holm wrote:
>Just checked the WX0B website and his 4 SQ box.
>As far as I remembered it used to use the Lewallen
>current forcing method however now he is talking
>about "the new Lahlum" method. Anyone know what
>that is? Sure looks like current forcing to me.
>Or do I have to wait until 2005 to read it in ON4UN´s
>book.
>
>73 Jim SM2EKM
Looking at the photo, I'd imagine it's a set of multiple LC networks, 
rather than a single network as used in the W7EL. This lets you do a bit 
better job synthesizing the phases, and potentially could remove the 
requirement for 1/4 wavelength lines, which creates a bit of a installation 
problem.  For instance,you could use 1/2 wavelength cables.


Unfortunately, the manual is a dead link(404), so I can't comment further.

This is a good compromise solution when you want to have your switching 
centralized, and with a reasonably symmetric array.  You do have potential 
loss from circulating currents in the feedlines. The reactive component to 
cancel the feedpoint reactive component is back at the box, so the reactive 
power is carried in the feedline.  In an ideal system, you'd have the 
reactance at the antenna, so that the feedline is at 50 ohms, and all the 
box needs to do is generate the right phases.  Of course, the matching 
network at the antenna would then need to have multiple values, since the 
feedpoint impedance changes with the array steering direction.  And, it 
would be quite "challenging" to tune up (broadcast antenna engineers earn 
their pennies doing this).

It would also make the total system cost higher.